A federal appeals court has affirmed the USDA’s policy of certifying hydroponic crop growers as “organic” even though the practice doesn’t improve soil fertility.

The 9th U.S. Circuit Court of Appeals has rejected arguments by critics who claimed the Organic Food Production Act prohibits hydroponic methods from certification.

“If the OFPA’s clearly barred hydroponic production, we would be required to enforce it according to its terms and set aside USDA’s interpretation,” the 9th Circuit said. “But no part of the statute clearly precludes organic certification of crops grown hydroponically.”

The dispute over hydroponics — in which crops are grown in perlite or another medium, often in large greenhouses — has been brewing for years in the organic community.

Critics claim the practice undermines the fundamental organic tenet of building soil fertility, but hydroponic supporters say opponents are simply afraid of competition from highly efficient producers.

The Center for Food Safety nonprofit and other critics petitioned the USDA to revoke organic certification from hydroponic growers, but the agency denied the request and a federal judge upheld that decision last year.

During oral arguments in July, the plaintiffs told a three-judge panel of the 9th Circuit that USDA’s policy has subverted the OFPA’s goal of ensuring consistent practices in the organic market.

“We have two sets of identical tomatoes, except only some of them live up to the true meaning of organic,” said Sylvia Wu, the Center for Food Safety’s attorney.

Consumers expect organically labeled crops to be grown according to standards for soil health specifically required by the OFPA, she said. Hydroponic crops by definition cannot meet those standards because they’re not grown in soil.

“The words ‘organic’ and ‘organic farming’ refer to soil organic matter,” Wu said. “So soil-building is the foundation of the environmental benefits that consumers associate with the organic label.”

The USDA countered that OFPA’s soil fertility provisions only apply to crops that are grown in the ground, but do not actually ban hydroponic methods.

If the law was intended to prohibit soil-free practices from organic certification, it could have done so directly rather than through oblique provisions related to soil health, said David Winik, the USDA’s attorney.

“That would have been a surpassingly strange way for Congress to create a soil requirement, if soil were as central to organic production as plaintiffs suggest,” he said.

The three-judge 9th Circuit panel has now unanimously agreed with the USDA, ruling that the law doesn’t require the agency to impose a regulation barring hydroponic methods.

The OFPA mandates that producers follow an organic plan and grow crops on land that hasn’t been treated with prohibited substances, while restricting their use of synthetic chemicals, the ruling said. It does not, however, specifically ban hydroponic methods.

The USDA’s acceptance of hydroponic methods is consistent with the OFPA’s approach of allowing practices unless they’re specifically banned, the 9th Circuit said.

The USDA has sufficiently “explained its reasoning” for its interpretation to be entitled to deference, even if certain experts disagree with the conclusion, the appellate court said.

“But expert opinion is not a reason for us to reverse the district court, much less second-guess USDA,” the ruling said.